development of the thermo-chemical and electrolytic hybrid ... · development of the...

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Development of the thermoDevelopment of the thermo--chemical and chemical and electrolytic hybrid hydrogen production processelectrolytic hybrid hydrogen production process

for sodium cooled FBRfor sodium cooled FBR

Third OECD/NEA Information Exchange Meeting on the Nuclear Production of Hydrogen

October 2005, O-Arai, Japan

Toshio NAKAGIRI, Takeshi KASE, Shoichi KATO and Kazumi AOTO

Japan Atomic Energy Agency

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Items

ObjectiveLong time hydrogen production experimentTechnical problems to develop higher performance (1NL/h-H2) hydrogen production systemConclusions

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To confirm the durability of the hydrogen production experimental apparatus with the hybrid process

To extract technical problems to develop higher performance (1NL/h-H2) hydrogen production system

ObjectiveObjective

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Principle of HHLTPrinciple of HHLT

HHLT HHLT (thermo-chemical and electrolytic Hybrid Hydrogen process in Lower Temperature range )2H2O + SO2 -> H2SO4 + H2 <100oC (electrolysis:0.17v) [1]H2SO4 -> H2O + SO3 400oC (thermal decomposition) [2]SO3 -> SO2 + 1/2O2 500-550oC (electrolysis:0.13v) [3]

Westinghouse processWestinghouse processSO3 -> SO2 + 1/2O2 >800oC (thermal decomposition) [3]’

・The hybrid process consists of H2SO4 synthesis and decompositionreactions. (Based on “Westinghouse process”)

・Maximum operation temperature is about 500-550oC.・Hydrogen and oxygen are produced from water.

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Electrolytic SO3 splitting with oxygen conductive solid electrolyte

Splitting voltage of SOSplitting voltage of SO33 is is 0.13V at 500oC.

-0.5

0.0

0.5

1.0

1.5

0 500 1000

Temperature(℃)

Spl

itting

voltag

e (V

)

EG, H2O

EG, SO3

Thermal decomposition fraction Thermal decomposition fraction of SOof SO33

0

0.2

0.4

0.6

0.8

1

0 500 1000 1500

Temperature (℃)

Decom

posi

tion fra

ction (-)

equilibrium

50%O2 removed

90%O2 removed

Splitting voltages of HSplitting voltages of H22O and SOO and SO33

(oC)(oC)

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Electrolytic SO3 splitting with oxygen conductive solid electrolyte

0

50

100

150

200

250

0 0.25 0.5 0.75 1 1.25

Cell voltage (V)

Cell

curr

ent (

mA

)

600℃550℃

500℃450℃

electrolyzer

SO3 evaporator（20-30°C）

Pressurecontroller

Flow meter

N2

SO3 + N2

O2 purge line N2

SO3, SO2 collector(gas bubbling )

O2 conc.

Potensiostat

O2 + N2

Solid electrolyte (YSZ)O2

electrolyzer

SO3 evaporator（20-30°C）

Pressurecontroller

Flow meter

N2

SO3 + N2

O2 purge line N2

SO3, SO2 collector(gas bubbling )

O2 conc.

Potensiostat

O2 + N2

Solid electrolyte (YSZ)O2

Relationship between cell voltage Relationship between cell voltage and cell currentand cell current

Electrolytic SO3 splitting was confirmed experimentally.

Test apparatus of SOTest apparatus of SO33 splitting experimentsplitting experiment

( 20 - 30oC )

oCoCoCoC

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Stable hydrogen and oxygen generation (max. 5hours) by HHLT was already confirmed by JNC.

- 50- 40- 30- 20- 10

01020304050

0 0.5 1 1.5 2 2.5

試験時間（h）

発生電流（mA）

RUN1

亜硫酸電極部（印加電位－0.34V）SO3電極部（印加電圧＋0.75V）

水素発生速度 5ml/h

- 50- 40- 30- 20- 10

01020304050

0 0.5 1 1.5 2 2.5

試験時間（h）


RUN1



Mea

sure

d cu

rren

t (m

A)

Time (h)

H2 generation rate (5ml/h)

H2SO3 solution electrolysis cellSO3 electrolysis cell

- 50- 40- 30- 20- 10

01020304050

0 0.5 1 1.5 2 2.5

試験時間（h）


RUN1



- 50- 40- 30- 20- 10

01020304050

0 0.5 1 1.5 2 2.5

試験時間（h）


RUN1



Mea

sure

d cu

rren

t (m

A)

Time (h)



- 50- 40- 30- 20- 10

01020304050

0 1 2 3 4 5 6

試験時間（h）



RUN7


- 50- 40- 30- 20- 10

01020304050

0 1 2 3 4 5 6

試験時間（h）



RUN7


Mea

sure

d cu

rrent

(mA

)

Time (h)



- 50- 40- 30- 20- 10

01020304050

0 1 2 3 4 5 6

試験時間（h）



RUN7


- 50- 40- 30- 20- 10

01020304050

0 1 2 3 4 5 6

試験時間（h）



RUN7


Mea

sure

d cu

rrent

(mA

)

Time (h)



Confirmation of hydrogen production by HHLT (previous experiments)

Measured cell current in previous experimentsMeasured cell current in previous experiments(for principle confirmation)(for principle confirmation)

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Potensio-stat

Water tank

O2 meter －＋

R

H2SO3 solution

electrolysis cell

Reference electrode

H2SO4 vaporizer

SO3 electrolysis

cell

SO2 absober

anode cathode

NaOH solution

Potensio-stat

－＋

Ｐ

Ｐ

H2SO3H 2

SO3

N2

SO2 +

H 2O SO3 + H2O

O2

H2SO4

H2

550℃O2

H2Ｐ

400℃

H2O2

Cooling tiller

：PumpＰ

N2 purge

10℃

Room Temp.

H2 collector

Experimental apparatus for hydrogen production

Long time hydrogen production experimentLong time hydrogen production experimentPt/8YSZ/Pt

Anolyte, Catholyte:50wt%H2SO4

H+ membrane: Nafion117

10 oC

550 oC

400oC

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Improvement of experimental apparatusImprovement of experimental apparatus

Improvement of SO3 electrolysis cell

・Pt electrode was manufactured by plating on both side of YSZ

・Diameter of the outlet piping of SO3 electrolysis cell was increased. (1/2 inch -> 3/4 inch)

-> Cell current at same cell voltage increased to 10 times.

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Experimental conditions

Reactor Temperature(deg-C)

Cell voltage(V)

H2SO4 vaporizer 400 -SO3 electrolysis

cell550 0.13

SO2 absorber Approx. 10 -H2SO3 solution

electrolysis cell

Room Temp. 0.85～0.9

Experimental conditionsExperimental conditions

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Experimental result

0

5

10

15

20

0 10 20 30 40 50 60 70

H2

O2

time (h)

Gen

erat

ion

rate

of H

2an

d O

2(m

l/h)

0

5

10

15

20

0 10 20 30 40 50 60 70

H2

O2

time (h)

Gen

erat

ion

rate

of H

2an

d O

2(m

l/h)

Total duration of present experiment was about 56 hours .(terminated by blockage of inlet pipe of SO2 absorber)

H2SO3 solution was added in the anolyte at about 20 and 40 hours after the experiment started.The anode surface was polished by emery paper at about 20 hours after, and stirring by N2 gas bubbling around the anode was started at about 40 hours after.

Generation rate of H2 and O2

H2SO3anodepolished

anode N2bubbling

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no plated gold remainedinner surface of outlet piping

of SO3 electrolysis cell

thickness of plated gold decreased.

to SO2 absorber

from H2SO4 vaporizer

inside surface of YSZ tube

Post experiment observation

Cut image of outlet piping of SO3 electrolysis cell

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Post experiment analysis

Blockage of the inlet pipe of SOBlockage of the inlet pipe of SO22 absorber absorber

whitepowder

SO2absorber

inlet pipe of SO2 absorber

SO2 absorber while powder in the inlet pipe

element weight fraction(wt%)

S 56.07Cr 6.35Fe 33.97Cu 3.61

Composition of white powder in the SO2 absorber by SEM-EDS analysis

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The performance of Pt plated YSZ electrolyte for SO3electrolysis did not degrade during about 60 hour operation in 550deg-C gaseous sulfuric acid. Outlet piping of the SO3 electrolysis cell was corroded by condensed sulfuric acid. Sulfuric acid resistant material (high Silicon cast iron,...) should be used in the new experimental apparatus.The hydrogen production rate in H2SO3 solution electrolysis cell for decreased in several hours, and the amount of H2SO3 solution supplied to the anode surface is considered to be not enough.

Long time hydrogen production experiment

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The performance of Pt plated YSZ electrolyte was about one order higher than YSZ with Pt paste electrode. The thickness of the Pt plated electrode is much thinner than Pt paste electrode, and SO3 or O2 molecule diffusion on the Pt plated electrode surface to the reaction area called three phase (gas/electrode/electrolyte) boundary is assumed to be much faster than on Pt paste electrode

Technical problems (1)-development of higher performance SO3 electrolysis cell-

SEM images of Pt paste and Pt plated electrodes

(×1000)

20μm20μm20μm 20μm20μm20μm

cross section

electrode surface

Pt paste electrode Pt plated electrode

electrode surface

cross section

Total area of three phase boundarymust be increased for higher performance.-thinner Pt plating electrode-smaller size Pt particle (catalyst)-mixed conductive electrolyte (ceria etc.)

YSZPt YSZPt

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flow rate of mixture gas (ml/min)

mea

sure

d ce

ll cu

rren

t (A

)

Improvement to increase the amount of H2SO3 solution or SO2 gas supplied to the anode surface.Use of flow type electrolysis cell with gas diffusion type electrode is promising.

Technical problems (2)-development of higher performance of

H2SO3 solution electrolysis cell-

Relationship between mixture gas (5%SO2+N2) flow rate and cell current (preliminary experiment)

Image of flow type electrolysis cell

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Conclusions

The experiment for about 60 hours was performed to investigate the durability of the experimental apparatus by the hybrid process.Technical problems to develop higher performance hydrogen production system were extracted.1NL/h-H2 production experiment are going to be performed in fiscal year 2005.

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